Subterranean network structures are provided in suburban locations. These networks may include telecommunications network cables, or gas or water pipes laid beneath pavements or roads. Trenches are typically dug when installing or maintaining these networks. These trenches are typically 1-1.5 m wide, 1.5 m deep and several meters long. It is often desirable to provide support structures to prevent trench walls from collapsing or to prevent debris coming away from the trench wall and contaminating a maintenance site. In some geographical regions, these preventative measures may be compulsory depending on local building regulations.
One possibility for supporting a trench wall is with the use of an Acrow prop, or ‘prop’. A prop includes a telescopic tube extending intermediate opposing feet extending generally transversely to the tube. Such props come in a range of sizes and a range of standard sizes. For example, a size 0 Acrow has a closed length of 1.04 m and an expanded length of 1.83 m. A size 4 Acrow has a closed length of 3.2 m and an open length of 4.88 m. A size 0 Acrow would be most desirable for use in supporting trench walls since the width of a trench is usually 1-1.5 m as described above.
In order to use the prop, a board is required to provide a load bearing surface for the prop and transmit a load exerted by the prop to a trench wall. Such an arrangement would require opposing boards each arranged to lie vertically against an opposing wall of the trench. This arrangement requires at least two personnel to perform various tasks for assembly. One person is required to erect opposing boards against the respective trench walls and then to hold a prop horizontally with opposing feet in the vicinity of each board. Another person is then required to extend the prop whilst the other holds it. Accordingly, even though the required equipment is simple and relatively cheap, the installation time and cost is unsatisfactory due to the number of people required.
One alternative mechanism which aims to address these problems includes two boards which are forced against opposing trench walls by a pair of pneumatic jacks. The pneumatic jacks are fixed to opposing end beams arranged to traverse the height of the trench walls to apply pressure across each board. This type of mechanism is pre-assembled and so also required more than one person to use since the size and shape of the mechanism is awkward for a single person to install. In addition, this type of pneumatic system is expensive, requires a pneumatic supply source for operation, and is rather complex.
It is an object of the present invention to address these problems and improve on the prior art.